The coating mass distribution from a 150 mm diameter spouted bed coater was studied. Three types of seed were coated with two types of fertilizer at various feed slurry rates, total coating mass added and spouting air velocity. The coating mass distribution was strongly dependent on the initial particle size distribution. The amount of coating on a particle was proportional to its mass. Over the range covered, spouted bed process parameters (slurry rate and spouting air velocity) had no effect on the coating mass distribution. A population balance model was developed to predict the coating mass distribution. This model, using a size dependent growth term, gave excellent agreement with experimentally measured coating mass distributions for all data sets. Model predictions were not as good using a size independent linear growth term. At this stage, it is not obvious why the larger particles are coated preferentially. The population balance model was extended to predict the coating mass distribution from a continuous spouted bed coater with both representative overflow and with overflow depending on particle mass.